Good to see that more votes keep coming in, even the anticipated vote for Mastodon! *grin* ;)
And I have to mix myself here in the discussion about whether or not Iron Maiden belongs in the Metal genre... short answer would be: They definitely do! But to elaborate a little more, since some are not persuaded yet, here's the official metal tree with Iron Maiden mentioned under 'New Wave of British Heavy Metal' (1979 - 1983)

More information about the whole Metal genre can be found in this Wikipedia article about the DVD documentary "Metal: A Headbanger's Journey".
There...
Now on with the competition!!!
@ LamprimOF : I counted your vote this time, but your reasoning is too thin. Make sure you add an obligatory elaborated reasoning for the next vote you state, ok? =)
@ susilo : You voted for Metallica, but this band is not featured in the current battle, which is between Pantera and Mastodon, so please vote for one of these two contestants with a reasoning, thanx! ;)
The vote count shows an extended lead for Pantera! They sure took off without looking back... O.o
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# 1/2 Final B :
6 - Pantera
1 - Mastodon
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Let's keep them votes coming people! The more the merrier!! =D